1. Field of the Invention
The present invention relates to a color photographic light-sensitive material containing a novel silver halide emulsion and a method of developing the same.
2. Description of the Related Art
Various silver halide photographic light-sensitive materials are put into practical use by utilizing the fact that silver halide crystal grains are sensitive to radiation such as visible light or ultraviolet rays to form a latent image and the latent image is converted into a visible image by development. Examples of a silver halide are silver iodide, silver bromide, silver chloride, and their mixed crystals. In this case, a silver halide to be used is selected in accordance with the application and the required function of a light-sensitive material in which the silver halide is used. For example, silver iodobromide grains having a relatively large grain size are used in a photographing light-sensitive material which must have high sensitivity. To the contrary, silver iodobromide or silver chlorobromide having a small grain size is used in a duplicating or printing light-sensitive material having relatively low sensitivity. A type of silver halide, a shape of crystals, a size of grains, and the like are important factors in determining properties of a silver halide emulsion. This is described in "The Theory of the Photographic Process" by T. H. James, 4th. ed. Macmillan Co. Ltd. New York, 1977, "Die Grundlagen der Photographischen Prozesse mit Silberhalogeniden" by C. Hasse, H. Frieser, and E. Klein, Akademische Verlagsgesellschaft, Frankfurt an Main, 1968, or the like.
Recently, printing and developing times of a printing light-sensitive material have been reduced. Therefore, a strong demand has increasingly arisen for a light-sensitive material which has high sensitivity and can be stably processed. Conventionally, a silver chlorobromide emulsion subjected to sulfur sensitization is practically used as a printing light-sensitive material. However, when a silver chlorobromide emulsion is used, a developing time cannot be reduced because development is significantly restrained by bromide ions released during development. In addition, since these ions are accumulated in a processing liquid, variations in photographic characteristics are increased. Furthermore, since the silver chlorobromide emulsion has low solubility in water, a long fixing time is required. A high silver chloride emulsion having a high silver chloride content and containing substantially no silver iodide is known as a preferable material for reducing a time required for development, bleaching, and fixing steps and for minimizing changes in photographic characteristics caused by variations in processing conditions. In a high silver chloride emulsion, cubic grains having a (100) crystal plane are normally formed. When these grains are chemically sensitized, they tend to cause fog. This fog is significant especially when the grains are subjected to gold sensitization. More specifically, fog poses a practical problem in a color developer having high activity for rapid development. Storage fogging generated when a light-sensitive material is storaged also poses a practical problem. When a high silver chloride emulsion is exposed at high intensity for a short period of time, a reciprocity failure is increased. This is another drawback of a high silver chloride emulsion when it is used as a printing material.
It is known that a high silver chloride emulsion of a regular crystal having a (111) crystal plane can be prepared by a special method. However, researches for such a method are not so many. F. H. Claes et al., Journal of Photographic Science, Vol. 21, Page 39 (1973) reports that silver chloride grains having the (111) crystal plane can be prepared using dimethyl thiourea. However, this report does not refer to a photographic property of the grains. D. Wyrsch reported in International Congress of Photographic Science (Rochester 1978) that grains having the (111) crystal plane can be prepared using a cadmium compound and ammonium. He reported that when photographic sensitivities of grains having the (111) crystal plane and those having the (100) crystal plane are compared with each other using a sulfur sensitizer, the grains having the (100) crystal plane have a slightly higher sensitivity although a large difference is not found. ("JP-A-" means unexamined published Japanese patent application, and "JP-B-" means examined Japanese patent application.) JP-A-55-26589 discloses that silver chloride octanhedral grains having the (111) crystal plane can be obtained in the presence of a merocyanine dye after nuclei are formed in grain formation. However, this patent specification describes only an effectiveness of adding a dye not in an initial stage of grain formation but at a predetermined timing thereof, regardress of a crystal plane or a composition of the grain. Therefore, although it is well known that a high silver chloride emulsion is a preferable material for reducing the time required for the processing steps, it is assumed to be technically difficult to use a high silver chloride light-sensitive material because fog is significant and a high-intensity failure is large when chemical sensitization is sufficiently performed in order to achieve high sensitivity. In addition, fog is naturally increased when gold sensitization is performed in order to improve the high-intensity failure. Therefore, no technique has been achieved to sufficiently perform gold plus sulfur sensitization with a high silver chloride emulsion.
It is well known to those skilled in the art that a so-called tabular grain having a grain size much larger than a grain thickness is preferred in order to increase sensitivity of a silver halide photographic emulsion and to increase sharpness, graininess, and a spectral sensitization efficiency and a coating power of a sensitizing dye.
Silver halide grains having a high silver chloride content (to be referred to high silver chloride grains hereinafter) tend to be cubic grains. Therefore, in order to obtain tabular grains, some techniques must be used. Examples of a method of obtaining high silver chloride tabular grains having a silver chloride content of 50 mol % or more are only a method disclosed in U.S. Pat. No. 4,399,215 in which grains are formed so as not to contain a bromide and an iodide under conditions of a pAg of 6.5 to 10 and a pH of 8 to 10; and a method disclosed in U.S. Pat. No. 4,400,463 in which grains are formed in the presence of an aminoazaindene and peptizer having an thioether bond.
Both of these patent specifications disclose a method of forming silver chloride tabular grains having a high aspect ratio and a large grain size, as can be seen from the examples. An emulsion having a high aspect ratio and a large grain size is advantageous in increasing an amount of a spectral sensitizing dye to be adsorbed in one grain. However, this emulsion is not preferably used in rapid development which is an object of the present invention. In addition, an emulsion having a high aspect ratio and a large grain size is disadvantageous in handling properties such as stress marks and stress desensitization which are essential in tabular grains and therefore is not preferable in practical use.
Furthermore, an increase in surface area of the grains does not lead to an increase in spectral sensitivity. Improving adsorption of a sensitizing dye is an important technique when a high silver chloride emulsion, especially a high silver chloride tabular emulsion is used. Moreover, spectral sensitivity cannot be improved without a technique of overcoming an inefficiency such as desensitization of instinct sensitivity caused when a large amount of a dye is used.
For these reasons, a strong demand has arisen for a high silver chloride grain which has a rapid development aptitude in addition to basic characteristics of, e.g., high sensitivity and less fog and satisfies practical conditions of, e.g., graininess and a response to stress.